The invention relates to a method for filling a fluid friction clutch housing to a desired degree with a viscous liquid medium, the clutch having sets of clutch plates and drive and driven sides, and to a device for practicing the method.
Fluid friction clutches of the above type are known for example from German patent No. 2,135,791. Their mode of operation is based on the principle, among others, that the high-viscosity liquid medium, consisting preferably of silicone oil, for example polysiloxane, placed in a clutch housing hermetically sealed from the outside, upon rotation of the sets of clutch plates relative to each other, builds up shear stresses owing to its viscosity, which oppose rotation of the sets of plates. The magnitude of these shear stresses and hence the magnitude of the torque transmitted depend, among other parameters, on the degree of fill of the housing with the liquid medium.
The use of such fluid friction clutches, for example in the transmission train of a motor vehicle, requires a precise adjustment of the clutch characteristic, that is, the torque transmission of the clutch or its gradient as a function of time, as well as a matching of speed between the drive and driven sides as a function of time.
These parameters may indeed be tuned by fixing the degree of fill of the clutch housing with liquid medium, but difficulties are involved in determining and/or setting the precise degree of fill of the housing. These difficulties of accurate proportioning reside in the fact that owing to manufacturing tolerances on the clutch parts, there may be internal volume tolerances amounting to a multiple of the allowable fill tolerance. Another problem consists in that deviations in the preassigned fill of the housing cannot be ascertained until such clutches are run on the test stand, when these errors can be rectified only by on-the-spot refilling and recalibration of the clutch.